support the submodule method

[nicolasochem]

We have the ability to deploy custom helm charts.

We need to preserve the ability to deploy custom images as well.

Allow passing custom paths for all tezos-k8s-images. When a custom path is given, use docker.buildAndPushImage to build it and pass the resulting image URL to the helm chart values.

This way we can keep having submodules in oxheadinfra whenever needed.